States / Colorado
45 counties · median score 10
Crawl space moisture in Colorado
Most of Colorado drains well: only 0 of 45 counties score high or elevated, and the median is 10. Alamosa County is the exception at 31; crawl-space moisture problems here usually come from grading, gutters and plumbing rather than the soil itself.
- 1Wettest county Alamosa County
- 2High or elevated 0 of 45
- 3Median score 10
- 4Driest county Yuma County
Colorado's soil, taken as a whole
Across the 44,977,697 acres mapped in these 45 counties, 3% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 4% of acres report a seasonal water table within about two metres. That is a dry figure; wet soils here are confined to river bottoms and wetlands. 44 of the 45 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 6.6% |
| Somewhat excessively drained | 5.5% |
| Well drained | 83.8% |
| Moderately well drained | 1% |
| Somewhat poorly drained | 1.3% |
| Poorly drained | 1.6% |
| Very poorly drained | 0.1% |
Radon. By EPA zone, 38 Colorado counties here are zone 1 (highest potential), 7 zone 2 and 0 zone 3. With most of the state in zone 1, any crawl-space sealing project here should start with a radon test and be designed to take a radon fan.
Every Colorado county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the Colorado numbers
The wettest county, Alamosa County, is 31% well drained by dominant condition, with a seasonal water table averaging 3.2 ft below grade across the 67% of acres that report one, and sits in EPA radon zone 2. The driest, Yuma County, is 62% well drained. No Colorado county reaches the high tier.
The score is a guide to the soil, not to a house: a well-graded lot with working gutters in a high county can have a dry crawl space, and a bad downspout can flood one in a low county. The R408 calculator sizes venting or encapsulation for any footprint.
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted; EPA Map of Radon Zones, county table (June 2024 JSON). Checked 2026-10-23.